Process cartridge and image forming apparatus

ABSTRACT

A process cartridge for an image forming apparatus includes a drum unit supporting a photosensitive drum; a developing roller; a driving roller for driving the roller; a drive receiving portion; a developing unit supporting the developing roller and the driving roller; and a connecting portion connecting the drum unit and the developing unit, the connecting portion being disposed below the driving roller. The developing unit is movable relative to the drum unit by rotating about the connecting portion between a contacting position in which the drum and the developing roller contact each other and a spacing position in which the drum and the developing roller are spaced from each other. A direction of the receiving portion is opposite to that of the developing roller, and is the same as the developing unit rotation from the spacing position toward the contacting position.

FIELD OF THE INVENTION AND RELATED ART

The present invention relates to a process cartridge detachablymountable to an image forming apparatus and an image forming apparatuscomprising the process cartridge. The image forming apparatus forms animage on a recording material using an image forming process. Examplesof the image forming apparatus include an printer, a copying machine, afacsimile machine, a wordprocessor and a complex machine having aplurality of functions of such machines.

Conventionally, in an image forming apparatus using anelectrophotographic image forming process, a photosensitive drum andprocess means actable on the photosensitive drum are unified into acartridge. The cartridge is detachably mountable to a main assembly ofthe image forming apparatus (process cartridge type).

Using the process cartridge type, the maintenance operations for theimage forming apparatus can be performed by the user without relying ona service person, and therefore, the operationality can be improvedremarkably, and the process cartridge type is widely used in an imageforming apparatus.

Japanese Patent 4464435 discloses an in-line type image formingapparatus in which a plurality of process cartridges are arranged in aline. Here, a process cartridge comprises a drum unit including thephotosensitive drum, and a developing unit including a developingroller, wherein the drum unit and the developing unit are connectedrotatably about a swing center.

The photosensitive drum is provided with a drum coupling at one endportion side of-the photosensitive drum with respect to the axialdirection of the photosensitive drum, and when the process cartridge ismounted to the main assembly of the apparatus, the drum coupling isengaged with a main assembly coupling provided in the main assembly ofthe apparatus to receive a driving force.

The developing roller is provided with an Oldham coupling as a shaftcoupling member at one end portion side of-the developing roller withrespect to the axial direction of the developing roller. When theprocess cartridge is mounted to the main assembly of the apparatus, adriving side engaging portion of the Oldham coupling is engaged with amain assembly development coupling provided in the main assembly of theapparatus to transmit the driving force to the developing roller.

Recently, a further image quality improvement of the image formingapparatus is desired. In a conventional example, a position of arotational center of the developing unit, a position of the driveinputting portion and a rotational moving direction thereof are soselected that an urging force of the developing roller to thephotosensitive drum by the weight of the developing unit and the drivingforce of the drive inputting portion of the developing unit decreases.

With such a structure, when the driving force is transmitted to thedeveloping roller, the urging force of the developing roller to thephotosensitive drum may be unstable.

The present invention is a further development of the prior-artstructure.

Accordingly, it is an object of the present invention to provide aprocess cartridge and an image forming apparatus in which a contactforce of the developing roller to the photosensitive drum is stabilized.

According to an aspect of the present invention, there is provided aprocess cartridge detachably mountable to an image forming apparatus,said process cartridge comprising a photosensitive drum: aphotosensitive unit rotatably supporting said photosensitive drum; arotatable developing roller for developing an electrostatic latent imageon said photosensitive drum; a driving roller for driving saiddeveloping roller; a drive receiving portion, provided below one endportion side of a shaft of said driving roller, for receiving a drivingforce from the image forming apparatus; a developing unit supportingsaid developing roller and said driving roller; and a connecting portionconnecting said photosensitive unit and said developing unit, saidconnecting portion being disposed below said driving roller with respectto the direction of gravity in a state that said process cartridge ismounted to the image forming apparatus, wherein said developing unit ismovable relative to said photosensitive unit by rotating about saidconnecting portion between a contacting position in which saidphotosensitive drum and said developing roller contact each other and aspacing position in which said photosensitive drum and said developingroller are spaced from each other, wherein a rotational moving directionof said drive receiving portion is opposite to that of said developingroller, and is the same as a direction of rotation of said developingunit from the spacing position toward the contacting position.

According to another aspect of the present invention, there is providedan image forming apparatus comprising a main assembly including adriving member for applying a driving force; a process cartridgedetachably mountable to said main assembly, said process cartridgeincluding a photosensitive drum, a photosensitive unit rotatablysupporting said photosensitive drum, a rotatable developing roller fordeveloping an electrostatic latent image on said photosensitive drum, adriving roller for driving said developing roller, a drive receivingportion, provided at one end portion side of a shaft of said drivingroller, for receiving a driving force by connecting with said drivingmember; a developing unit supporting said developing roller and saiddriving roller, a connecting portion connecting said photosensitive unitand said developing unit, said connecting portion being disposed belowsaid driving roller with respect to the direction of gravity in a statethat said process cartridge is mounted to the image forming apparatus,wherein said developing unit is movable relative to said photosensitiveunit by rotating about said connecting portion between a contactingposition in which said photosensitive drum and said developing rollercontact each other and a spacing position in which said photosensitivedrum and said developing roller are spaced from each other, wherein arotational moving direction of said drive receiving portion is oppositeto that of said developing roller, and is the same as a direction ofrotation of said developing unit from the spacing position toward thecontacting position.

Further features of the present invention will become apparent from thefollowing description of exemplary embodiments with reference to theattached drawings.

These and other objects, features and advantages of the presentinvention will become more apparent upon a consideration of thefollowing description of the preferred embodiments of the presentinvention taken in conjunction with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a principal sectional view of an image forming apparatus in anembodiment of the present invention.

FIG. 2 is a principal sectional view of a process cartridge in theembodiment.

FIG. 3 is a general perspective view of the process cartridge in theembodiment.

FIG. 4 is a general perspective view of a developing unit in theembodiment.

FIG. 5 is a perspective view showing a state in which a processcartridge is mounted to the image forming apparatus in the embodiment.

FIG. 6 is a sectional view for illustrating a spacing operation of thedeveloping unit in the embodiment.

FIG. 7 is a sectional view for illustrating a contact operation of thedeveloping unit in the embodiment.

FIG. 8 is a side view for illustrating a relationship between adeveloping unit rotation center and developing drive input position androtational direction in a conventional constitution.

FIG. 9 is a side view for illustrating a relationship between adeveloping unit rotation center and developing drive input position androtational direction in the embodiment.

FIG. 10 is a side view showing another constitution example in theembodiment.

DESCRIPTION OF THE EMBODIMENTS

Embodiments of the present invention will be specifically described withreference to the drawings.

(General Structure of Image Forming Apparatus)

FIG. 1 is a sectional view showing a general structure of an imageforming apparatus 100 according to an embodiment of the presentinvention. As shown in FIG. 1, four process cartridges 70 (70Y, 70M,70C, 70K) for executing a part of an image forming process aredetachably mounted to a main assembly of the image forming apparatus100. Incidentally, the process cartridges 70Y, 70M, 70C and 70K arecollectively referred to as the process cartridge 70. In the following,also the members are similarly described. Further, an upstream side ofthe process cartridge 70 with respect to a mounting direction of theimage forming apparatus 100 is defined as a front (surface) side, and adownstream side of the process cartridge 70 with respect to the mountingdirection is defined as a rear (surface) side.

In FIG. 1, the respective process cartridges 70 are inclined andjuxtaposed in an apparatus main assembly 100A with respect to ahorizontal direction ht. Incidentally, a direction g in FIG. 1 is thedirection of gravitation.

The process cartridge 70 includes a photosensitive drum 1 (1 a, 1 b, 1c, 1 d) for bearing a toner image. At a periphery of the photosensitivedrum 1, including a charging roller 2 (2 a, 2 b, 2 c, 2 d), a developingroller 25 (25 a, 25 b, 25 c, 25 d), and a cleaning member 6 (6 a, 6 b, 6c, 6 d) are integrally provided.

The charging roller 2 electrically charges the surface of thephotosensitive drum 1 uniformly, and the developing roller 25 develops alatent image, formed on the photosensitive drum 1, with a toner(developer) to visualize the latent image. The cleaning member 6 removesthe toner remaining on the photosensitive drum 1 after a toner imageformed on the photosensitive drum 1 is transferred onto a recordingmaterial (medium).

Further, below the process cartridges 70, a scanner unit 3 for formingthe latent image on the photosensitive drums 1 by subjecting thephotosensitive drums 1 to selective exposure to light on the basis ofimage information is provided.

At a lower portion of the apparatus main assembly 100A with respect tothe direction g of gravitation, a cassette 99 in which sheets of therecording material S are accommodated is mounted. Further, a recordingmaterial conveying means is provided so that the recording material Scan be conveyed to an upper portion of the apparatus main assembly 100Aby being passed through a secondary transfer roller 69 and a fixingportion 74. That is, a feeding roller 54 for separating and feeding thesheets of the recording material S in the cassette 99 in a one-by-onemanner, a conveying roller pair 76 for conveying the fed recordingmaterial S, and a registration roller pair 55 for synchronizing thelatent image formed on the photosensitive drum 1 with the recordingmaterial S are provided.

Further, above the process cartridges 70, an intermediary transfer unit5 onto which the toner image formed on each of the photosensitive drums1 is to be transferred is provided. The intermediary transfer unit 5includes a driving roller 56, a follower roller 57, primary transferrollers 58 (58 a, 58 b, 58 c, 58 d) opposing the photosensitive drums 1for the respective colors, and an opposite roller 59 opposing thesecondary transfer roller 69 are provided. Around these rollers, atransfer belt 9 is extended and stretched. Further, the transfer belt 9is circulated and moved so as to be contacted to all of thephotosensitive drums 1, so that primary transfer of the toner imagesfrom the photosensitive drums 1 onto the transfer belt 9 is made. Then,by voltage application to the secondary transfer roller 69 and theopposite roller 59 disposed inside the transfer belt 9, the toner imagesare transferred from the transfer belt 9 onto the recording material S.

During image formation, while rotating the photosensitive drum 1, thephotosensitive drum 1 uniformly charged by the charging roller 2 issubjected to selective exposure to light emitted from the scanner unit3, so that an electrostatic latent image is formed on the photosensitivedrum 1. The latent image is developed by the developing roller 25, sothat the toner images of the respective colors (Y, M, C, Bk) are formedon the associated photosensitive drums 1, respectively.

In synchronism with this image formation, the registration roller pair55 conveys the recording material S to a secondary transfer positionwhere the secondary transfer roller 69 opposing the opposite roller 59is contacted to the transfer belt 9. At this secondary transferposition, the respective color toner images are secondary-transferredfrom the transfer belt 9 onto the recording material S, so that a colorimage is formed on the recording material.

The recording material S on which the color image is formed is heatedand pressed by the fixing portion 74, so that the color image (tonerimages) is fixed on the recording material S. Thereafter, the recordingmaterial S is discharged onto a discharge portion 75 by a(sheet-)discharging roller pair 72.

(Process Cartridge)

Next, the process cartridge 70 in this embodiment will be described withreference to FIGS. 2 to 4.

FIG. 2 is a principal sectional view of the process cartridge 70 inwhich the toner is accommodated, and FIG. 3 is a perspective view of theprocess cartridge 70.

Incidentally, the process cartridge 70Y accommodating the toner ofyellow (Y), the process cartridge 70M accommodating the toner of magenta(M), the process cartridge 70C accommodating the toner of cyan (C), andthe process cartridge 70K accommodating the toner of black (Bk) have thesame constitution.

The respective process cartridges 70 include photosensitive (drum) units26 (26 a, 26 b, 26 c, 26 d) and developing units 4 (4 a, 4 b, 4 c, 4 d).The photosensitive unit 26 includes the photosensitive drum 1, thecharging roller 2 and the cleaning member 6. Further, the developingunit 4 includes the developing roller 25.

To a cleaning frame 37 of the photosensitive unit 26, the photosensitivedrum 1 is rotatably mounted via a front drum bearing 10 (FIG. 3) and arear drum bearing 11 (FIG. 3). The photosensitive drum 1 is providedwith a drum coupling 16 (FIG. 3) at an end portion thereof.

[Photosensitive Unit]

The cleaning member 6 provided on the peripheral side of thephotosensitive drum 1 is constituted by an elastic member 6 a formedwith a rubber blade and a cleaning supporting member 6 b. A residualtoner removed from the surface of the photosensitive drum 1 by thecleaning member 6 falls into a removed toner chamber 27 a.

By transmitting a driving force of a driving motor (not shown) to thephotosensitive unit 26, so that the photosensitive drum 1 isrotationally driven depending on an image forming operation. Thecharging roller 2 is rotatably mounted to the photosensitive unit 26 viaa charging roller bearing 28 and is urged against the photosensitivedrum 1 by a charging roller urging member 46, thus being rotated by therotation of the photosensitive drum 1.

[Developing Unit]

The developing unit 4 is constituted by the developing roller 26,rotated in contact with the photosensitive drum 1 and a developingdevice frame 31 for supporting the developing roller 25. Further, thedeveloping unit 4 is constituted by a developing chamber 31 b in whichthe developing roller 25 is disposed and toner accommodating chamber 31c, disposed below the developing chamber 31 b, for accommodating thetoner. These chambers are partitioned by a partition wall 31 d. Further,the partition wall 31 d is provided with an opening 31 e through whichthe toner passes when the toner is fed from the toner accommodatingchamber 31 c to the developing chamber 31 b.

The developing roller 25 is rotatably supported by the developing(device) frame 31 via a front developing (means) bearing 12 (FIG. 4) anda rear developing (means) bearing 13 (FIG. 4) provided in both sides ofthe developing device frame 31, respectively.

Further, on a peripheral surface of the developing roller 25, adeveloper supplying roller 34 rotatable in contact with the developingroller 25, and a developing blade 35 for regulating a toner layer on thedeveloping roller 25 are provided. The developer supplying roller 34 isconstituted by a metal-made developer supplying roller shaft 34 a and asponge portion 34 b, and the sponge portion 34 b is disposed in contactwith the developing roller 25 with a predetermined penetration amountinto the developing roller 25.

Further, in a toner accommodating chamber 31 c in the developing frame31, a toner feeding member 36 for feeding the toner into the developingchamber 31 b through the opening 31 e while stirring the toneraccommodated in the toner accommodating chamber 31 c is provided.

[Connection Between Photosensitive Unit and Developing Unit]

FIG. 3 is a general perspective view of the process cartridge 70. To thephotosensitive unit 26, the developing unit 4 is rotatably mounted. Afront supporting pin 14 and a rear supporting pin 15 (FIG. 2) which arepress-fitted in the cleaning frame 27 are engaged with hand holes 12 aand 13 a (FIGS. 2 and 4), respectively, of the rear developing bearing13 (FIG. 4). As a result, the developing unit 4 is rotatably supportedby the cleaning frame 27 with the front supporting pin 14 and the rearsupporting pin 15 are rotation shafts.

Further, the cleaning frame 27 is provided with a front drum bearing 10and a rear drum bearing 11 which rotatably support the photosensitivedrum 1. The rear drum bearing 11 supports a drum coupling 16 coupled tothe photosensitive drum 1. Further, the front drum bearing 10 supports aflange 17. Here, the drum coupling 16 is a drum coupling member fortransmitting a rotational force from the apparatus main assembly 100A tothe photosensitive drum 1.

Further, FIG. 4 is a general perspective view of the developing unit 4.The developing frame 31 is provided with the front and rear developingbearings 12 and 13 for rotatably supporting the developing roller 25.Further, the developing unit 4 is constituted so as to be urged againstthe photosensitive unit 26, during image formation of the processcartridge 70, by an urging spring 32 provided at each of ends of thedeveloping frame 31. By these urging spring 32, an urging force forbringing the developing roller 25 into contact with the photosensitivedrum 1 with, as rotation centers, the hang holes 12 a and 13 a of thefront and rear developing bearings 12 and 13 is generated.

(Insertion and Mounting of Process Cartridge into Image FormingApparatus Main Assembly)

FIG. 5 is a perspective view showing a state in which the processcartridge 70 is mounted to the apparatus main assembly 100A of the imageforming apparatus 100.

In this embodiment, a direction in which the process cartridge 70 isinserted through openings 101 (101 a, 101 b, 101 c, 101 d) of the imageforming apparatus 100 is a direction (arrow F direction in the figure)parallel to an axial direction of the photosensitive drum 1.

In this embodiment, with respect to an insertion direction of theprocess cartridge 70, an upstream side is defined as a front side, and adownstream side is defined as a rear side. Further, in the image formingapparatus 100, a guide portion 103 (103 a, 103 b, 103 c, 103 d) isprovided in an upper side, and a guide portion 102 (102 a, 102 b, 102 c,102 d) is provided in a lower side. The process cartridge 70 is placedin a front side of the guide portion 102 with respect to a mountingdirection and then is moved in the insertion direction indicated by thearrow F along the guide portions 102 and 103, thus being inserted intothe image forming apparatus 100.

(Contact and Separation Embodiment Photosensitive Drum and DevelopingRoller)

A spacing mechanism between the photosensitive drum 1 and the developingroller 25 in the process cartridge 70 will be described with referenceto FIGS. 6 and 7.

FIG. 6 is a sectional view showing the case where the photosensitivedrum 1 and the developing roller 25 are spaced from each other. In FIG.6, the apparatus main assembly 100A is provided with a spacing member 94constituting a spacing means at a predetermined position with respect toa longitudinal direction of the process cartridge 70. In the developingunit 4, a spacing force receiving portion 31 a of the developing frame31 receives a force from the spacing member 94 moving in an arrow Ndirection, thus rotating the developing unit 4 in a rotational direction(second rotational direction) in which the developing unit 4 is spaced.

For this reason, the developing roller 25 is moved to a spaced positionwhere the developing roller 25 is spaced from the photosensitive drum 1.

FIG. 7 is a sectional view showing the case where the photosensitivedrum 1 and the developing roller 25 are in contact with each other.

As shown in FIG. 7, when the spacing member 94 moves in an arrow Pdirection away from the spacing force receiving portion 31 a, thedeveloping unit 4 is rotated in an arrow T direction (first rotationaldirection) about the holes 12 a and 13 a of the front and reardeveloping bearings 12 and 13 by the urging force of the urging springs32 (FIG. 4) provided at the ends of the developing frame 31. Then, thedeveloping unit 4 is moved to a contact position, so that the developingroller 25 is contacted to the photosensitive drum 1.

By the spacing constitution shown in FIGS. 6 and 7, in a period otherthan during the image formation, the developing unit 4 is held at thespaced position shown in FIG. 6, so that the influence of deformation ofthe developing roller 25 on an image quality is suppressed.

(Relationship Between Developing Unit Rotation Center and DevelopingDrive Input Position and Rotational Direction)

A relationship between a rotational direction of a developing driveinput in the process cartridge 70 and a rotation center position of thedeveloping unit 4 will be described with reference to FIGS. 8 and 9.FIG. 8 is a side view for illustrating a relationship belt a developingunit rotation center and developing drive input position and rotationaldirection in a conventional constitution, and Figure is a side view forillustrating a relationship belt the developing unit rotation center andthe developing drive input position and rotational direction in thisembodiment.

First, a constitution of a conventional process cartridge will bedescribed with reference to FIG. 8. Incidentally, in this conventionalconstitution, portions identical or similar to those in this embodimentare represented by the same reference numerals or symbols and will beomitted from redundant description.

FIG. 8 is a sectional view showing the process cartridge mounted to amounting portion 101 of the image forming apparatus, and shows a statein which the developing roller 25 and the photosensitive drum 1 are incontact with each other. A rectilinear line L1 connecting a rotationshaft of the developing roller 25 with a rotation shaft of thephotosensitive drum 1 and a rectilinear line L2 extending from therotation shaft in the direction g of gravitation form a predeterminedangle θ1 which is closer to 90 degrees. In a state in which the processcartridge is mounted to the image forming apparatus main assembly, aconstitution in which a position of the photosensitive unit 26 is fixedand the developing unit 4 is rotated relative to the photosensitive unit26 is employed.

Further, when centers, as the rotation center of the developing unit, ofthe holes 12 a and 13 a of the front and rear developing bearings 12 and13 are taken as a rotation center Q (rotation shaft), the rotationcenter Q is disposed below the photosensitive drum 1 and the developingroller 25 with respect to the gravitation direction g. Further, when aposition of the center of gravity of the developing unit 4 is taken as abarycentric position R, with respect to the gravitation direction g, thebarycentric position R is disposed in the developing unit 4 side ratherthan the rotation center Q of the developing unit 4.

In this case, by the weight of the developing unit 4, a force ofrotation moment Q shown in FIG. 8 is applied to the developing unit 4.By rotation of the developing unit 4 in an arrow T direction, thephotosensitive drum 1 and the developing roller 25 are in contact witheach other, and therefore an urging force of the developing roller 25toward the photosensitive drum 1 acts in the arrow T direction. For thatreason, rotation moment Q2 thereof is directed in a direction ofdecreasing the urging force of the developing roller 25 toward thephotosensitive drum 1.

Further, in the conventional process cartridge, as shown in FIG. 8, adeveloping drive input portion is rotated in a rotational direction U2.For this reason, a force of rotation moment Q2 b is applied to thedeveloping unit 4. This direction is the direction of decreasing theurging force of the developing unit 4 toward the photosensitive drum 1.

Next, a constitution of the process cartridge in this embodiment of thepresent invention will be described with reference to FIG. 9.

FIG. 9 is a sectional view showing the process cartridge mounted to amounting portion 101 of the image forming apparatus, and shows a statein which the developing roller 25 and the photosensitive drum 1 are incontact with each other. In a cross section shown in FIG. 9, arectilinear line L3 connecting a rotation shaft of the developing roller25 with a rotation shaft of the photosensitive drum 1 and a rectilinearline L4 extending from the rotation shaft in the direction g ofgravitation form a predetermined angle θ2 which is closer to 90 degrees.In a state in which the process cartridge is mounted to the imageforming apparatus main assembly, a constitution in which a position ofthe photosensitive unit 26 is fixed and the developing unit 4 is rotatedrelative to the photosensitive unit 26 is employed.

When centers, as the rotation center of the developing unit, of theholes 12 a and 13 a of the front and rear developing bearings 12 and 13are taken as a rotation center Q, the rotation center Q is disposedbelow the photosensitive drum 1 and the developing roller 25 withrespect to the gravitation direction g.

The developing roller 25 and the developer supplying roller 34 arerotatably supported by the developing unit 4. Further, the developersupplying roller 34 is provided, at a rotation shaft thereof, with adeveloping drive input portion 23 (driven portion), and the developingdrive input portion 23 receives a rotational force from an outside torotate the developer supplying roller 34. Further, the developersupplying roller 34 not only supplies the developer to the developingroller 25 but also transmits the rotational force received from thedeveloping drive input portion 23. In this embodiment, a constitution inwhich the developer supplying roller 34 is contacted to and spaced fromthe developing roller 25 is not employed, but a constitution in which acontact state between the developer supplying roller 34 and thedeveloping roller 25 is maintained is employed.

The urging springs 32 (FIG. 4) urge between the developing unit 4 andthe photosensitive unit 26, so that the photosensitive drum 1 and thedeveloping roller 25 are placed in the contact state. By rotation of thedeveloping unit 4 in an arrow T direction, the photosensitive drum 1 andthe developing roller 25 are in contact with each other, and thereforean urging force of the developing roller 25 toward the photosensitivedrum 1 acts in the arrow T direction. Thus, by the contact between thephotosensitive drum 1 and the developing roller 25, during the imageformation, the developer is supplied from the developing roller 25 tothe peripheral side of the photosensitive drum 1.

On the other hand, during non-image formation, as described above withreference to FIGS. 6 and 7, from the outside of the process cartridge 70to the developing unit 4, a force is applied in an opposite direction tothe direction (arrow T direction) of the urging force of the urgingsprings 32 (FIG. 4), so that the photosensitive drum 1 and thedeveloping roller 25 are spaced from each other. As a result, it ispossible to prevent deformation or the like of the photosensitive drum 1at the peripheral side due to continuous urging of the developing roller25 against the photosensitive drum 1.

Further, when the position of the center of the developing unit 4 is abarycentric position R, the barycentric position R is disposed in thedeveloping unit 4 side rather than the rotation center Q of thedeveloping unit 4 with respect to the gravitation direction. In thiscase, by the self-weight of the developing unit 4, a force of rotationmoment Q1 a shown in FIG. 9 is applied to the developing unit 4. Thisdirection is a direction of decreasing the urging force of thedeveloping roller 25 toward the photosensitive drum 1. However, in thisembodiment, a rotational direction U1 of the developing drive inputportion 23 is the same as the rotational direction T of the developingunit 4. As a result, a force of rotation moment Q1 b is applied from thedeveloping drive input portion 23 to the developing unit 4. This forceis applied in a direction of increasing the urging force of thedeveloping roller 25 toward the photosensitive drum 1.

That is, in the conventional constitution, the moment by the self-weightof the developing unit 4 and the moment received by the rotation of thedeveloping roller 25 acted in the direction of decreasing the urgingforce of the developing roller 25 toward the photosensitive drum 1. Forthis reason, the urging of the developing roller 25 become unstable insome cases.

On the other hand, in this embodiment, the moment by the self-weight ofthe developing unit 4 and the moment received by the rotation of thedeveloping drive input portion are applied in opposite directions.

In this way, in the process cartridge 70 having a constitution in whichthe positions of the rotation center Q and the barycentric position R ofthe photosensitive unit 4 are in a position relationship such that theurging force of the developing roller 25 toward the photosensitive drum1 is decreased by the self-weight of the developing unit 4, thefollowing effect is achieved. That is, the rotational direction U1 ofthe developing drive input portion 23 is set at the direction ofincreasing the urging force of the developing roller 25 toward thephotosensitive drum 1, whereby the urging of the developing roller 25against the photosensitive drum 1 can be stably performed.

Incidentally, the developer supplying roller 34 is rotated in the samedirection as the first direction, and the angle θ2 is close to 90degrees, so that a force for rotating the developing unit 4 in the firstdirection is applied from the rotation shaft of the developer supplyingroller 34 to the developing unit 4.

Further, in this embodiment, the constitution in which the developingdrive input portion 23 is disposed on the axis of the developersupplying roller 34 was described.

However, as shown in FIG. 10, a constitution in which the developingdrive input portion 23 is not disposed on the axis of the developersupplying roller 34 may also be employed. That is, when the relationshipbetween the rotation center Q about which the developing unit 4 isrotated and the position and rotational direction of the developingdrive input portion 23 is such that the urging force of the developingroller 25 toward the photosensitive drum 1 is increased, a similareffect can be obtained.

In this case, when a driving roller 110 is driven in an arrow U3direction by the developing drive input portion 23, a rotational drivingforce is transmitted to a follower roller 120. At this time, the drivingroller 110 receives a force from the follower roller 120, so that momentQ3 b for rotating the developing unit 4 about the rotation center Q isgenerated. That is, the direction of the moment Q3 b is opposite to adirection of moment Q3 a for rotating the developing unit 4 about therotation center Q. For this reason, a force for decreasing the urgingforce of the developing roller 25 toward the photosensitive drum 1 canbe made small, so that the developing roller 25 can be stably urged.

While the invention has been described with reference to the structuresdisclosed herein, it is not confined to the details set forth and thisapplication is intended to cover such modifications or changes as maycome within the purpose of the improvements or the scope of thefollowing claims.

This application claims priority from Japanese Patent Application No.273206/2012 filed Dec. 14, 2012, which is hereby incorporated byreference.

1. A process cartridge detachably mountable to an image formingapparatus, said process cartridge comprising: a photosensitive drum; aphotosensitive unit rotatably supporting said photosensitive drum; arotatable developing roller for developing an electrostatic latent imageon said photosensitive drum; a driving roller for driving saiddeveloping roller; a drive receiving portion, provided below one endportion side of a shaft of said driving roller, for receiving a drivingforce from the image forming apparatus; a developing unit supportingsaid developing roller and said driving roller; and a connecting portionconnecting said photosensitive unit and said developing unit, saidconnecting portion being disposed below said driving roller with respectto the direction of gravity in a state that said process cartridge ismounted to the image forming apparatus, wherein said developing unit ismovable relative to said photosensitive unit by rotating about saidconnecting portion between a contacting position in which saidphotosensitive drum and said developing roller contact each other and aspacing position in which said photosensitive drum and said developingroller are spaced from each other, wherein a rotational moving directionof said drive receiving portion is opposite to that of said developingroller, and is the same as a direction of rotation of said developingunit from the spacing position toward the contacting position.